Years ago comcast introduced some speed boost thing. I forget what they called it. It was basically a docsis command they used to temporarily uncapped the modem. Every time it would kick in my modem would take a dive. I finally just purchased my own. They weren't getting any more of my rental fees and trying to convince them to send a new modem didn't work.
Next they were having problems with a particular router. Traceroute proved it. They didn't listen and it took weeks to fix.
Comcast isn't better because they have better support. Comcast is better because the technology now tells them when they have problems and the lemmings go and fix it.